Transcriptional feedback of Erk signaling waves in zebrafish scale regeneration

Regeneration requires long-range cellular coordination. In regenerating bony zebrafish scales, waves of activity of the Extracellular Receptor Related Kinase (Erk) induce growth of bone-forming tissue. Erk waves were proposed to result from an excitable system including feedback with Erk activators and inhibitors. Here, we characterize how Erk modulates its inhibitors, predicted to limit wave frequency and thus tissue growth. First, we found that Erk waves can form spirals, signature of excitable systems, and exhibit refractory behavior compatible with Erk inhibitors following Erk waves. Using a newly developed single-molecule fluorescence in situ hybridization (smFISH) technique for whole scales, we discovered that Erk waves induce trailing transcript waves of the inhibitors dusp5, spry2 and spry4 through Rectified Linear Unit (ReLU) responses. Furthermore, we discovered that Erk waves modulate transcription of the gene osterix, which controls maturation of bone-forming cells. This reveals a transcriptionally-encoded mechanism that couples Erk wave dynamics, and thus tissue growth, with scale maturation during regeneration.